A bit of confusion here I believe is that different species of kale obviously have different levels of vitamins, minerals, and oxalates.
The USDA used to state that a 100g serving of Kale had around 20mg of oxalate, which really isn't too much. However, a much more recent study has found Kale to actually be quite low, at 2mg per 1 cup chopped.(1)
However, we don't know which variety of Kale was actually used. That being said, there really are no other good sources out there from anything other than the typical health food blogger about how much oxalate content Kale has.
has quite a database which allows you to search for food items and it tells you the source of the data.
But, should we even care about oxalates? Well to a certain degree. Obviously we don't want to feed foods that are extremely high in oxalate content, such as rhubarb leaves. But, I think we are demonizing something here that doesn't really need to be demonized.
Collard greens for example, are touted as a great staple. They have ~400mg of oxalate per 100g (2)
. That's a lot more than even the old high numbers of kale were. But, you'd be hard pressed to get a dragon to even eat that much Collard. Harvard 2008 shows that 1 cup of collard is only 10mg of oxalate anyways.(2)
So if kale was only demonized for it's oxalate content, it was wrongly so.
Here is the thing - the body is a wonderful thing. It is more complicated than any of us could ever fathom. It has so many moving and working parts to it, that trying to figure out one thing often leads you down a path of dozens of more interactions and complications. Like the fact that Vitamin C can be converted into Oxalic acid in the body too. Does that mean that you should stop feeding foods that are high in Vitamin C? Absolutely not.
The body has ways of dealing with excess, and the body has ways (to a degree) of dealing with a lack of things. Kale provides a ton of health benefits, and a ton of micro-nutrition. To avoid it simply over one potential negative (all the while many other plants have the same issues) is silly in my opinion.
Lets remember here that most all vegetable leaves will have high(er) oxalate content. But that doesn't necessarily make them a bad choice.
But lets also remember, there is no one right way to raise our dragons. There is no 1 perfect diet.